Researchers in the Arctic Basin yesterday spotted a hugely fat pregnant polar bear female on broken ice over water about 2,500 meters deep. Some people seem to find this surprising but it’s what I discussed last week.
Photo above by Tim Kenna from aboard the Coast Guard cutter Healy. Researchers are in the area as part of the “TRACES of Change in the Arctic” program. Another perspective on the bear and the location it was spotted on 24 August 2015 below, as well as some background on Arctic Basin bears.
“When we venture into the Arctic for research, for most of us there is the lingering hope that a polar bear will appear on our watch; at least as long as we are safely outside of its reach. Several polar bear have been spotted by the watchful eyes of the crew as we have moved into the more tightly packed heavy ice away from the marginal ice zone. However, today a very large bear (yes the alert text says “huge”!) was spotted, and it seemed to have us under thoughtful consideration. The following is a string of images that relay the majesty of this incredible creature in its natural environment, moving with great agility over the sea ice.”
Another perspective of the bear, which is in excellent condition for a pregnant female, courtesy Tim Kenna. Is she a Southern Beaufort bear? Could be but no way to know for sure, as she doesn’t have a collar. Actually, that’s not surprising, since it’s clear that many SB females never come close enough to shore to become part of the tracked or counted subsample – see the study area in the map below, which is Fig. 1 from the Bromaghin et al. 2015 Southern Beaufort population estimate.
This is Fig. 1 from Bromaghin et al. 2014, showing the study area. Note about half of the Southern Beaufort Sea subpopulation is in the USA and the other half is in Canada. Canada has recently moved the eastern boundary to ~ Tuktoyaktuk.
Read the rest here, with more pictures. h/t AE Derocher
Below, background on Arctic Basin polar bears.
Bears in the Deep Arctic Basin
[NIPCC Summary of a report by Russian researcher Ovsyanikov 2010]
Ovsyanikov, N. 2010. Polar bear research on Wrangel Island and in the central Arctic Basin. In, Proceedings of the 15th meeting of the Polar Bear Specialists Group IUCN/SSC, 29 June-3 July, 2009, edited by Obbard, M.E., Theimann, G.W., Peacock, E. and DeBryn, T.D., pp. 171-178. Gland, Switzerland and Cambridge UK, IUCN.
“The late summer Arctic Basin surveys were split between two years, each taking a different route: the 2005 expedition surveyed northward from Wrangel Island (in the far eastern Russian Arctic), on both sides of the 180° meridian up to 79°15′ N, while the 2007 trip surveyed north from Franz Joseph Land (in the far western Russian Arctic, at about 81°N, 60°E), to the North Pole and back. Observations were taken 24hrs/day from the ship bridge for the duration of the trips and sightings of both bears and ringed seals were recorded.
In 2005, 18 bears were seen north of Wrangel, 12 of these above 75°N, which marks the edge of the continental shelf at this location. Ten of the bears seen were in four family groups and three of these families were observed north of the continental shelf. All were in good physical condition. A female and her single cub-of-the-year were observed feeding on a ringed seal at 78°50.20′ N, 177°27.40′ W, where water depth under the ice was 1500 m. In addition, seven tracks of lone bears were recorded north of the continental shelf. A total of 48 ringed seals were observed from Wrangel Island to 79°15′ N, more than half of these between 78°-79° N.
In 2007, the survey ship worked the other side of the Arctic Basin, north of Franz Joseph Land, where the continental shelf ends between 82°-83° N (Weber, 1983). Seven polar bears were sighted beyond 81° N, all of them in good condition and all recorded on fields of substantial ice. One female was observed and photographed at the North Pole on 1-2 August 2007. A total of 61 tracks of single bears were also recorded, with a concentration around 82° N. Eleven ringed seals were also observed, five between 82°-83° N, three between 83°-87° N and three between 89°-90° N (including one at the North Pole). A lower proportion of the observations of seals and bears were noted beyond the continental shelf north of Franz Joseph Land than were sighted north of Wrangel Island but a few seals and at least one bear were recorded close to, or at, the North Pole.
The deep water over the Arctic Basin is often assumed to be of such low productivity (e.g. Fischbach et al., 2007; Obbard et al., 2010) that it is largely unsuitable for polar bears except as a transit corridor. However, this assumption is contradicted by measurements of significant amounts of phytoplankton and ice algae (e.g. Gosselin et al., 1997; Stirling, 1997) as well as reports at the North Pole of “small fish” (estimated as 5-8cm, presumably young polar cod, Boreogadus saida) thrown up by ice-breakers and algal growth visible on the underside of broken ice chunks (Todd et al., 1992). Polar cod and their prey are the food of ringed seals and are known to live under ice of all types, including multi-year and first year drifting sea ice regardless of the ocean depth (Lønne and Gulliksen, 1989). The cracks (“leads”) that continuously develop in moving multiyear ice allow thinner first year ice to form, creating habitat for seals and thus potential food for polar bears (Stirling, 1997).
Ovsyanikov suggests that ringed seals living at the periphery of the Arctic Ocean move into the central Arctic Basin as the pack ice recedes in late summer and that polar bears which choose to stay on the pack ice (rather than moving onto land) move along with the seals and the ice into the central Arctic beyond the continental shelves. Previous reports have also documented the presence of both ringed seals (Todd et al., 1992) and polar bears in the central Arctic Basin (Van Meurs and Splettstoesser, 2003); in 1992-93, a female tracked via satellite by Durner and Amstrup (1995) migrated from Prudhoe Bay in the southern Beaufort to northern Greenland via the central Arctic Basin (going as far north as 88°).
Ovsyanikov’s Arctic Basin survey confirms that ringed seals and polar bears do not require ice that is positioned over shallow, continental shelf waters, although higher densities of both species undoubtedly exist in such areas (e.g. Derocher et al., 2004). Ovsyanikov’s study, although limited, is the first systematic look at polar bears and ringed seal abundance within the Arctic Basin. Further surveys may reveal that the Arctic Basin is a more important habitat for polar bears than has been assumed (e.g. Obbard et al., 2010).”
References
Bromaghin, J.F., McDonald, T.L., Stirling, I., Derocher, A.E., Richardson, E.S., Rehehr, E.V., Douglas, D.C., Durner, G.M., Atwood, T. and Amstrup, S.C. 2015. Polar bear population dynamics in the southern Beaufort Sea during a period of sea ice decline. Ecological Applications 25(3): 634-651. http://www.esajournals.org/doi/abs/10.1890/14-1129.1 [paywalled]
Derocher, A.E., Lunn, N.J. and Stirling, I. 2004. Polar bears in a warming climate. Integrative and Comparative Biology 44: 163-176.
Durner, G.M. and Amstrup, S.C. 1995. Movements of a polar bear from northern Alaska to northern Greenland. Arctic 48: 338-341.
Ferguson, S.H., Taylor, M.K. and Messier, F. 2000. Influence of sea ice dynamics on habitat selection by polar bears. Ecology 81: 761-772.
Fischbach, A.S., Amstrup, S.C. and Douglas 2007. D.C. Landward and eastward shift of Alaskan polar bear denning associated with recent sea ice changes. Polar Biology 30: 1395-1405.
Gosselin, M., Levasseur, M., Wheeler, P.A., Horner, R.A. and Booth, B.C. 1997. New measurements of phytoplankton and ice algae production in the Arctic Ocean. Deep-Sea Research II 44: 1623-1644.
Lønne, O.J. and Gulliksen, B. 1989. Size, age and diet of polar cod, Boreogadus saida (Lepechin 1773), in ice covered waters. Polar Biology 9: 187-191.
Mauritzen, M., Derocher, A.E. and Wiig, Ø. 2001. Space-use strategies of female polar bears in a dynamic sea ice habitat. Canadian Journal of Zoology 79: 1704-1713.
Obbard, M.E., Theimann, G.W., Peacock, E. and DeBryn, T.D. (eds.) 2010. Polar Bears: Proceedings of the 15th meeting of the Polar Bear Specialists Group IUCN/SSC, 29 June-3 July, 2009, Copenhagen, Denmark. Gland, Switzerland and Cambridge UK, IUCN.
Stirling, I. 1997. The importance of polynyas, ice edges, and leads to marine mammals and birds. Journal of Marine Systems 10: 9-21.
Todd, F.S., Headland, R.K. and Lasca, N. 1992. Animals at the North Pole. Polar Record 28: 321-322.
Van Meurs, R. and Splettstoesser, J.F. 2003. Farthest North Polar Bear (Letter to the Editor). Arctic 56: 309.
Weber, J.R. 1983. Maps of the Arctic Basin sea floor: A history of bathymetry and its interpretation. Arctic 36: 121-142.
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